Bulkhead connectors have been traditionally used for several decades primarily for subsurface, high temperature and pressure applications. These electrical connectors are provided to ensure connectivity with tools used in logging, completing, or during drilling of oil and gas wells. These tools consist of various electronic instruments contained within pressure housings which are maintained at atmospheric pressure. The electronics inside the pressure housing normally requires a hermetic type electrical connection that interconnects with electrical conductors (often in a wireline) to maintain communications with electronic instruments uphole normally at the surface. These hermetic connectors have contacts that can be either single-pin or multi-pin types depending upon the specific application. The connectors must also easily connect and disconnect and function as conduits for electrical conduction in extreme hostile liquid and gaseous environments that include exposure to brine, oil base drilling mud and fluids that may contain hydrogen sulfide, carbon dioxide, methane, and other corrosive elements as well as oil and gas at pressures often exceeding 25,000 psi and temperatures greater than 500° F.
These bulkhead connectors must also be constructed in such a way as to provide a hermetic seal capable of withstanding high differential pressures and temperatures in the presence of sudden or enduring shock and vibration, and maintain the ability to carry high voltages. Typically, when these specific connectors are exposed to borehole fluids, a rubber boot seal is used that fits over the male end of the connector contacts, thereby providing a moisture-free seal for the conductive contact(s) (or pins). Another possibility exists when these connectors are used inside the tools, in that the connectors could be used to seal against hydraulic oil used to hydrostatic pressure balance the mechanical section of the tools. In these cases, the bulkhead connector must also be capable of withstanding high differential pressure without a rubber boot seal. Similar issues exist regarding the need to protect the contacts from shock and vibration which occurs in the downhole environment.
A major source of electrical signal distortion or failure using these bulkhead connectors is associated with the original purpose of their design. Namely, the one or more contacts (pins) that protrude from the bulkhead surface (male portion) of the connector toward a receiving section of the connector (female portion or socket) are subject to extremely high shear forces during operation in harsh (shock and vibration) environments. This often leads to one or more of the electrical contacts being either severed or severely compromised, as the pins protruding from the bulkhead may be completely “cross-cut” or sheared. The contacts of the connector thereby no longer provide the required electrical connectivity for the device(s). Current bulkhead designs provide an absolute absence of the ability for flexure of the pin and socket arrangement(s). In fact, current designs are intended to be completely fixed and rigid so that there can be no movement either before or after the two ends of the connector are mated, helping to ensure the hermetic seal. These connectors can be hermaphroditic in that male pins can slide by one another, a pin and socket may exist on the same connector, or the connector may be a simple pin and socket arrangement.
In at least some instances, to avoid or at least diminish the possibility of absolute mechanical failure due to shear, the two bulkhead contact ends (pin and socket ends) are intentionally spaced apart by using a partial gap between the two outer portions of the bulkhead. Separation of this type, in some applications, leads to reduction of absolute shear failure incidents as the shear forces acting directly on the contact(s) is slightly reduced. One tradeoff in using this technique is that the bulkhead no longer provides the intended hermetic seal integrity for which it was originally designed. This can lead to premature contact failure due to the corrosive environments in which the connectors operate. Also, this technique results in a reduction and loss of contact area, leading to an increase in resistivity that is concurrent with a loss in power reduction and/or signal integrity.
A typical single pin type connector to which the invention pertains includes a conductive pin in the center covered by an insulating material which in turn is encased in a body. Single pin hermetic connectors made from polymers have been known to exist at least as early as since 1985. Halliburton Logging Services, Inc., Halliburton Co., made electrical connectors from Fiberite FM-4005F resin phenolic by both transfer mold and injection mold techniques. These connectors were limited to a maximum of 20,000 psi and are similar to the present invention including the fact that the pin can be threaded or press fit into the body. The body is usually formed from thermoplastics or thermoset polymers. This type construction is limited by the strength of the polymer bond (often epoxy) which results in deformation of the plastic body at high pressure and temperature. Furthermore, an interference fit of the pin in the body could damage the plastic body during assembly resulting in a high scrap rate which increases manufacturing costs.
Multi-pin connectors have also been manufactured using polymers since at least the early 1990's for existing high pressure and temperature applications in down hole applications. The multiple-pin plastic connectors have been designed to withstand pressure to 28,000 psi at 510° F. for numerous cycles. These designs provided an advantage in that plastic is not a rigid material. The plastic construction has forgiving characteristics that at high temperatures will relax and adjust to thermal expansion of primarily the bulkhead body without causing the multi-pin connector to fail due to harsh environments. Plastic single-pin connectors exhibit this same forgiving characteristic.
However, due to the enormous stresses generated due to shock and vibration, the need to distribute (primarily shearing) stresses acting on a single point is critical to avoid shearing of the contacts extending outwardly from the connector. Even though the stresses are generally more uniform for single contact (pin) connectors with respect to the geometric pin configuration, multiple pin connectors, which are more sensitive to temperature distribution anomalies and small manufacturing defects, should be also designed to survive the stresses described.